Recycling phosphogypsum as a sole calcium oxide source in calcium sulfoaluminate cement and its environmental effects

As the disposal of phosphogypsum can result in severe contamination of soil and groundwater, several researchers worldwide have devoted efforts toward realizing suitable methods for PG disposal. This study demonstrates the feasibility of using phosphogypsum as the sole CaO source in the preparation of calcium sulfoaluminate cement by considering its mechanical properties and the potential environmental impacts of its large-scale utilization. First, the effects of the alumina/silica ratio on the mineral phase formation, setting time, compressive strength, and microstructure of calcium sulfoaluminate cement were studied. An alumina/silica ratio of 2.0 or 2.5 resulted in satisfactory mineral phase formation and compressive strength; the compressive strength of calcium sulfoaluminate cement reached 63.2, 88.5, and 100.2 MPa after 1, 3, and 28 d of curing, respectively. Second, the environmental behaviors of harmful impurities in the raw materials and calcium sulfoaluminate cement were investigated. In the static leaching and acid leaching tests, the concentrations of harmful elements in the calcium sulfoaluminate cement leachates met the requirements of national standards (GB/T14848-2007). After a period of curing, P and some heavy metals (Mn, Cr, Ni, Cu, and As) did not leach from the cement. Finally, a novel process and a system of preparing CSA cement by using phosphogypsum as the sole CaO source are proposed. This novel technology could be employed as a reliable and environment friendly means of recycling phosphogypsum in the large-scale preparation of calcium sulfoaluminate cement.